A microwave generator of the type here contemplated comprises a stationary electrode structure in a housing, this structure forming an array of evacuated resonant cavities centered on an axis. In order to adjust the frequency of the generated microwaves, each cavity is provided with a metallic plunger which can be introduced into it to a greater or lesser extend through the axial displacement of a tuning disk rigid with these plungers. The cavities and their plungers are usually cylindrical and are separated from each other by a small annular clearance. Thus, the plungers must be precisely guided and must not undergo any significant dimensional changes in order to avoid short circuits, arcing or spurious resonances due to parasitic capacitances. Severe defromations may even result in a jamming of the plungers in their cavities.
Since the operation of a magnetron-type oscillator generates considerable heat, the apparatus must be effectively cooled to prevent such dimensional changes. Heretofore, separate cooling means have been used for the stationary components, including the electrode structure, and the movable components, i.e. the tuning mechanism. In one such conventional system, hydraulic fluid is circulated around the anode and cathode of the electrode structure, which constitutes the principal heat source, whereas the tuning device is air-cooled by means of a finned hollow cylinder which rests on the movable disk and is filled with a heat-exchanging fluid.
While the use of a dual cooling system obviates the problem of fluidically linking the stationary and movable components of the magnetron, its drawback is the limited thermal capacity of the aforedescribed heat exchanger which may cause overheating of the plungers with all the attendant difficulties.